The dogs barked and the caravan moved on

Does anyone know the origin and meaning of the saying "then the dogs barked and the caravan moved on"? I think it may have been used by an Australian Prime Minister, Paul Keating, in recent times (post late 1990's) but it may have some previous form.

Dogs bark, but the caravan goes on. Only found it in one quote book and it was called a late 19th century proverb, not attributed to anyone. "Oxford Dictionary of Quotations," Fifth Edition, edited by Elizabeth Knowles (Oxford University Press, Oxford and New York, 2001). Page 598.